Although a ‘fast’ strategy may enhance the speed of range expansion (Burton et al.
2010), ‘slow’ cycles protect species from the dramatic loss of genetic variability
during upward migration: when a few founders colonise a remote patch, delayed
maturation allows genetic diversity to accumulate through recruitment of additional
individuals (Austerlitz et al. 2000). It is also often argued that alpine specialists
inhabiting narrow elevation bands may lack substantial genetic variability for traits
under selection, but evidence of this phenomenon is not strong, because the distribution of these species is the result of past climate-driven shifts up and down elevation
gradients that helped maintain genetic differentiation (Galbreath et al. 2009; Wachter
et al. 2012). Hence, predicting evolutionary trajectories into the future must take into
account the past persistence of many relict species (Hampe and Petit 2005).
The interactions between climate shifts with phenotypic plasticity or heritable
variation in reaction norms are also crucial to envisage species responses to
changing environmental conditions (Winkler et al. 2002; Both and Visser 2005;
Jensen et al. 2008; Williams et al. 2015). Temperature increases may not necessarily have the expected worst impact on ectotherm metabolism because they may
adjust thermoregulation and activity to prevailing temperatures (Aguado and Braña
2014), as alpine plants do with respiration (Larigauderie and Körner 1995). It is also
worth stressing that warming reduces some of those constraints dominating alpine
life, as evidenced by improved survival or reproductive output of a number of
species (e.g. Day et al. 1999; Erschbamer 2007; Ozgul et al. 2010). Similarly,
Barrett et al. (2015), using data from a long-term research project in the Arctic,
demonstrated enhanced reproductive allocation in connection with improved air
and soil temperature. Differences in species’ responses are, however, huge, making
generalisations of responses and predictions of effects very weak. Experiments and
observations within the same community or environmental context often highlight
highly idiosyncratic responses in growth and reproduction to changing temperature
and resource availability (Wookey et al. 1993; Arft et al. 1999; Dorman and
Woodin 2002; Wipf et al. 2009).
11.6.3 Demographic Responses to Environmental Change
Patterns of life history determine the dynamics of populations when facing environmental variation, and life-history traits have a differential influence in this
process. Perturbations (either cyclic or stochastic) can trigger substantial fluctuations in population size when reproductive parameters have the greatest influence
on the finite rate of population growth, corresponding to a ‘fast’ life strategy. In
contrast, perturbations are buffered when survival parameters have the largest relative influence on growth rate, i.e. a ‘slow’ strategy (Sæther and Bakke 2000; Oli
and Dobson 2003). Therefore, when facing environmental change, a ‘slow’ life
strategy is expected to confer more stable dynamics, high resistance and low
resilience, as opposed to a ‘fast’ life strategy, which induces more cyclic or chaotic
11 Life-History Responses to the Altitudinal Gradient
273
2010), ‘slow’ cycles protect species from the dramatic loss of genetic variability
during upward migration: when a few founders colonise a remote patch, delayed
maturation allows genetic diversity to accumulate through recruitment of additional
individuals (Austerlitz et al. 2000). It is also often argued that alpine specialists
inhabiting narrow elevation bands may lack substantial genetic variability for traits
under selection, but evidence of this phenomenon is not strong, because the distribution of these species is the result of past climate-driven shifts up and down elevation
gradients that helped maintain genetic differentiation (Galbreath et al. 2009; Wachter
et al. 2012). Hence, predicting evolutionary trajectories into the future must take into
account the past persistence of many relict species (Hampe and Petit 2005).
The interactions between climate shifts with phenotypic plasticity or heritable
variation in reaction norms are also crucial to envisage species responses to
changing environmental conditions (Winkler et al. 2002; Both and Visser 2005;
Jensen et al. 2008; Williams et al. 2015). Temperature increases may not necessarily have the expected worst impact on ectotherm metabolism because they may
adjust thermoregulation and activity to prevailing temperatures (Aguado and Braña
2014), as alpine plants do with respiration (Larigauderie and Körner 1995). It is also
worth stressing that warming reduces some of those constraints dominating alpine
life, as evidenced by improved survival or reproductive output of a number of
species (e.g. Day et al. 1999; Erschbamer 2007; Ozgul et al. 2010). Similarly,
Barrett et al. (2015), using data from a long-term research project in the Arctic,
demonstrated enhanced reproductive allocation in connection with improved air
and soil temperature. Differences in species’ responses are, however, huge, making
generalisations of responses and predictions of effects very weak. Experiments and
observations within the same community or environmental context often highlight
highly idiosyncratic responses in growth and reproduction to changing temperature
and resource availability (Wookey et al. 1993; Arft et al. 1999; Dorman and
Woodin 2002; Wipf et al. 2009).
11.6.3 Demographic Responses to Environmental Change
Patterns of life history determine the dynamics of populations when facing environmental variation, and life-history traits have a differential influence in this
process. Perturbations (either cyclic or stochastic) can trigger substantial fluctuations in population size when reproductive parameters have the greatest influence
on the finite rate of population growth, corresponding to a ‘fast’ life strategy. In
contrast, perturbations are buffered when survival parameters have the largest relative influence on growth rate, i.e. a ‘slow’ strategy (Sæther and Bakke 2000; Oli
and Dobson 2003). Therefore, when facing environmental change, a ‘slow’ life
strategy is expected to confer more stable dynamics, high resistance and low
resilience, as opposed to a ‘fast’ life strategy, which induces more cyclic or chaotic
11 Life-History Responses to the Altitudinal Gradient
273